This invention relates generally to semiconductor devices, and in particular, a semiconductor device having a p-n junction with a photosensitive region that can be modulated with an optical source to generate hole-electron pairs from a partial depletion region formed within the photosensitive region when the p-n junction is subjected to a reverse bias voltage. The generation of hole electron pairs in the photosensitive region causes current to flow between the p-n junction. The semiconductor device is particularly useful for power amplification, and has improved linearity.
Linearity in radio frequency (RF)/microwave power amplifiers is an important characteristic in the design of these devices. Poor linearity in power amplifiers can have many adverse effects. For instance, poor linearity can result in harmonic, intermodulation, and signal compression distortions, to name a few. Thus, designers of power amplifiers continue to develop new techniques for improving the linear characteristic of power amplifiers.
Traditionally, two types of field effect transistors have been used for RF/microwave power amplifications. These are the metal-oxide semiconductor field effect transistor (MOSFET) and the gallium-arsenide Metal-semiconductor field effect transistor (GaAs MESFET). MOSFETs are used in power amplification purposes because they are typically easier to manufacturer and are less expensive. However, they have poor linear characteristics which requires linearization compensation which adds to the cost and efficiency of the overall product. GaAs MESFETs, on the other hand, are more frequently employed for RF/microwave power amplification applications due to their improved linearity characteristic over MOSFETs. However, they are typically expensive due to complexity in their manufacturing processes.
Thus, there is a need for a new semiconductor device that uses MOSFET technology for manufacturing purposes in order to reduce cost, but has improved linearity such as that provided by GaAs MESFETs.
One aspect of the invention includes a semiconductor device that has a p-n junction with a photosensitive region partially having a depletion region and a non-depletion region when the p-n junction is subjected to a reverse bias voltage. When an incident light (e.g. a laser) is directed at the surface of the photosensitive region, hole-electron pairs are generated within the depleted region within the photosensitive region. As a result, the current through photosensitive region occurs which varies in a substantially linear fashion with the intensity of the incident light. The semiconductor device can be configured in a circuit to provide substantially linear power amplification.
A more specific exemplary embodiment of the semiconductor device comprises a substrate, n-doped and p-doped regions within the substrate, and a channel formed between the n-doped and p-doped regions. As with all p-n junction, a depletion region exists within the channel when a reverse bias voltage is applied across the p-n junction. The semiconductor device further includes a photosensitive region situated within the channel in a manner that it includes a boundary of the depletion region when the reverse bias voltage is applied across the p-n junction. The partial depletion region within the photosensitive region generates hole-electron pairs in response to an incident light upon the photosensitive region.
A more broader concept of the invention includes a semiconductor device having a substrate including a channel for conduction of current, wherein the channel includes a depletion region during the conduction of current (the depletion region exists with or without current flow), a photosensitive region situated within the channel in a manner that it includes a boundary of the depletion region during the conduction of current. Hole-electron pairs are generated within the depletion region within the photosensitive region in response to an incident light upon the photosensitive region. The device need not be limited to reverse bias diode configuration, and can encompass other configurations.
Another aspect of the invention includes an amplifier that uses the semiconductor device of the invention. The amplifier comprises a modulator for modulating a light with an input signal and a semiconductor device in accordance with the invention. The semiconductor device receives the modulated light signal which modulates the current through the semiconductor device. The semiconductor device is connected across a bias voltage with a series bias impedance to generate current through the semiconductor device. The current generates an output voltage that is an amplified version of the input signal.
Another aspect of the invention includes a complimentary device having a p-channel photosensitive semiconductor device in accordance with the invention and an n-channel photosensitive semiconductor device in accordance with the invention. An optic fiber channel is provided to couple an optical signal to respective photosensitive regions of the p-channel and n-channel devices. The p-doped region of the p-channel device and the n-doped region of the n-channel device are electrically coupled to the same potential, preferably a ground potential. The p-channel device is biased with a positive voltage (+Vd) through a series resistive element, and the n-channel device is biased with a negative voltage (xe2x88x92Vd) also through a series impedance element. When an optical signal is applied to the complimentary devices by way of the optical fiber or lens, the complimentary devices operate in a push-pull manner. The complimentary devices can be used for many applications.
Another aspect of the invention includes a complimentary device having a p-channel photosensitive semiconductor device in accordance with the invention and an n-channel photosensitive semiconductor device in accordance with the invention. An optic fiber channel is provided to couple an optical signal to respective photosensitive regions of the p-channel and n-channel devices. A first impedance element is connected to the n-doped region of the p-channel device at one end, and to the n-doped region of the n-channel device at the other end. A second impedance element is connected to the p-doped region of the p-channel device at one end, and to the p-doped region of the n-channel device at the other end. A first bias voltage is applied to the n-doped region of the n-channel device, and a second bias voltage is applied to the p-doped region of the p-channel device. The first bias voltage is more positive than the second bias voltage. Preferably, the second bias voltage is at ground potential. When an optical signal is applied to the complimentary devices by way of the optical fiber or lens, the complimentary devices operate in a push-pull manner.
Another aspect of the invention includes a semiconductor device configured for a push-pull operation. The semiconductor device includes a p-n junction with a photosensitive semiconductor material in accordance with the invention. An optic fiber channel is provided to couple an optical signal to the photosensitive region of the device. A first impedance element is connected to the n-doped region of the device, and second impedance element is connected to the p-doped region of the device. A first bias voltage is applied to the n-doped region by way of the first impedance device, and a second bias voltage is applied to the p-doped region by way of the second impedance device. The first bias voltage is more positive than the second bias voltage. Preferably, the second bias voltage is at ground potential. When an optical signal is applied to the device by way of the optical fiber or lens, the device causes opposite flowing currents through the first and second impedance elements to effect the push-pull operation.
Other aspects of the invention will become apparent in view of the following detailed discussion of the invention.